Not only did the freshman senator face a challenger with an unusual financial advantage, he also beat back what Republicans had hoped would be a decisive issue in Pennsylvania and other coal states across the nation: that President Obama and the Democrats were waging a war on coal that hurt jobs and the economy.

"While we came up a little big short tonight, let me tell you it remains the same: We must repeal Obamacare. We must stop deficit spending. We must end this war on American energy, this war on Pennsylvania coal. And most importantly, we must get this economy roaring again," Mr. Smith said in his concession speech Tuesday night.

With a war chest of some $20.3 million, Smith mounted an aggressive television ad campaign that dubbed Senator Casey as "the invisible senator," who hadn't passed a single bill in six years, "even to help jobs." A newcomer to politics, Smith brought the race to within single digits, but was never able to overcome the incumbency advantage and Casey's popularity in the state.

A centrist with a conservative record on social issues, Casey, who raised $12.5 million, never fell behind in the race. He appeared to engage the challenger relatively late in the race, after polls signaled that Smith was making gains. His ad campaigns dubbed Smith a "tea party extremist" whose coal mines endangered workers.

A former state treasurer and the son of a former governor, Casey launched his first Senate bid with significant name recognition the strong support of the national party establishment, eager to find a candidate who could defeat then-Sen. Rick Santorum. His support of conservative social issues, especially his opposition to abortion rights, riled many liberals in Democratic Party ranks, but also made him a tough target for GOP challengers, including Smith this year and Senator Santorum, who were both held to 41 percent of the vote.

Exit polling signals that 6 in 10 Pennsylvania voters called the economy their top issue, with only 1 in 8 concerned about deficits – a leading GOP issue. Just over half of voters said that government was doing too many things better left to businesses and individuals. Independent voters fell out evenly between Casey and Smith, according to the Associated Press.